Effect of superplasticizers on workability retention and initial setting time of cement pastes

This paper presents an experimental study on the effect of a newly developed modified lignosulphonate (PLS) superplasticizer on the loss of workability and initial setting time of cement pastes in comparison to those of polycarboxylate (PCE) and polynaphthalene (PNS) superplasticizers. The workability loss was monitored by yield stress and effective viscosity of the pastes. The initial setting was monitored by heat development, change of rheological parameters with time, and penetration depth in cement pastes. The relations among these methods were discussed. Different dosages of the superplasticizers were used to obtain cement pastes with yield stress <6 Pa at 30 min at given water-to-cement ratios. The results showed that the pastes with PLS lost workability more slowly and had longer initial setting time compared with those with PCE and PNS admixtures. Although the longer workable time is beneficial for hot weather concreting, the longer initial setting time of such material has to be taken into consideration where early strength development is essential.